Flexible borehole liners are installed by the eversion process to seal a borehole against flow into or out of the borehole, which flow can cause the spread of ground water contamination. The installation method as commonly practiced propagates an everting borehole liner into the hole by adding water to the interior of the everting liner, which dilates the liner and, as the liner is everted into the borehole, causes the liner to displace the borehole fluids (usually water or air) into the adjacent surrounding subsurface formation. The installation of the liner, and/or its placement after installation, permits the gathering of a variety of useful data regarding subsurface conditions in the vicinity of the borehole. Aspects of the data-gathering process may include measuring or monitoring water level(s) in the borehole; some boreholes are in fact monitoring “wells.” Helpful and general background regarding the utility and function of everting flexible borehole liners is provided by applicant's previously issued U.S. Pat. Nos. 5,176,207, 6,283,209, and 6,910,374, which are incorporated herein by reference.
Most water level measurements in traditional wells are performed by lowering a pressure transducer beneath the water surface to monitor the pressure history of water level changes. A multi-level sampling system in a single borehole does not allow such a simple measurement of the formation head at different levels in the formation. Previously known flexible liner systems for multi-level water sampling and head measurements in a single borehole use pressure transducers dedicated to the system and located significant distances (e.g., 100-200 feet) below the water table in a borehole in the geologic formation. Such pressure transducers monitor the hydraulic head in the formation at many different elevations. However, if one (or more) transducer should fail, the entire multi-level system must be removed from the borehole to access and replace the failed transducers. This removal, besides causing delay and expense, can result in damage to other functioning transducers, as well as to the flexible liner sampling system.
Flexible liner designs for a multi-level sampling system have been known for years, but previous designs have involved deep transducer locations, with transducers inaccessibly situated down-well, sometimes hundreds of feet, and more or less permanently dedicated to the system. Applicant's previously known “Water FLUTe” system is described at http://www.flut.com/sys 1.html, (incorporated herein by reference). Certainly the multi-level water sampling system has been improved beyond the teachings of applicant's U.S. Pat. No. 5,176,207, or of applicant's co-pending U.S. patent application Ser. No. 12/001,801 entitled “Pore Fluid Sampling System with Diffusion Barrier.” The cost of removal and repair of failed transducers in known systems, however, can be a major expense of the design. Also, the dedication of the transducers to the system is a very expensive feature of the system, and the transducers are not available for reuse in other applications.
Improvements in transducer accuracy, and the recent addition of data recording capability in an individual transducer, increase significantly the practicality of the presently disclosed apparatus and method compared to systems using formerly utilized, less-accurate, transducers. That fact, coupled with the peculiar needs of the multi-level sampling system, were the background for the formulation of the useful devices and methods hereinafter disclosed.